Box filter



FIG. 1 is a side elevational view of a box filter, showing my new design, the opposite elevational view being a mirror immage thereof; the broken line showing is for illustrative purposes only and forms no part of the claimed design;

FIG. 2 is a right end elevataional view thereof;

FIG. 3 is a left end elevational view thereof; and,

FIG. 4 is a top plan view thereof, the bottom plan view being identical thereto. 

The ornamental design for a box filter, as shown and described. 